Many of the automobiles being produced today are equipped with a hydraulic brake system including an anti-lock brake subsystem for assuring that the vehicle wheels do not lock up during sudden applications of the brake. The anti-lock brake system (ABS) is considered by many to be the most significant improvement in vehicle safety within the last decade and it is presently being offered as standard equipment in many vehicles.
Most types of ABS include a singular hydraulic control unit, usually in the form of an aluminum block, in which there is incorporated all of the componentry necessary to provide the anti-lock braking function to the braking system. This includes solenoid actuated isolation valves for isolating a particular wheel brake from braking force exerted through the brake pedal and master cylinder. It also includes solenoid actuated hold/dump valves which are opened to relieve braking pressure at each of the wheel brakes thereby allowing the brake to relax its hold on the wheel. It further includes several low pressure accumulators and a pump for providing supplemental brake pressure to the wheels during the period of controlled braking.
All of this componentry is located in a single control unit, which is typically an aluminum block bored as required to receive the components and to provide fluid communication between the valves, accumulators, and pump to complete the hydraulic circuitry. Consequently, the control unit can be of considerable size and complexity from a manufacturing viewpoint, in that a considerable number of machining operations are required. Amongst these machining requirements, is that of threading each of the bores which are to receive a control valve. Typically for one ABS unit this requires twelve separate threading operations.
Likewise, each of the control valves must be similarly threaded. Furthermore, it is standard practice in the design and manufacture of the isolation control valves and hold/dump valves to provide for securing the internal valve seat or pole piece to the outer concentric valve body or sleeve by a threaded connection, thereby requiring two additional threading operations in the manufacture of a single control valve. The thread cutting operation in the design of the control valves also requires further steps in the manufacturing process to assure that metal shavings are eliminated as any such foreign matter may impeded the flow of brake fluid within the valve.
A typical control valve of the type described above as being part of the prior art is shown in FIG. 2 herein. The same general structure can be seen in U.S. Pat. No. 4,828,335, assigned to the assignee of the present invention, which is incorporated herein by reference as a teaching of the prior art ABS control valve devices and methods of making same.